Conventional air bags are produced by coating or laminating a plain weave fabric, formed by weaving nylon 66 or nylon 6 filament yarns of 300 to 1000 deniers (330 to 1100 dtex), with an elastomer resin such as a synthetic rubber, for example chloroprene, chlorosulfonated olefin or silicone, to provide a base fabric with improved heat resistance, flame resistance, gas interceptability, etc., and cutting and sewing the base fabric into bags.
When the plain weave fabric is coated or laminated with such an elastomer resin, a coating process such as knife coating, roll coating or reverse coating, is generally adopted. If the plain weave fabric made from filaments is coated with a chloroprene elastomer resin, to make the base fabric, the resin is applied to the surface of the base fabric in an amount of 90 to 120 g/m.sup.2, and the air bag produced is very heavy, hard and coarse in appearance. If the air bag is inflated to contact the face of the passenger, he/she can be scratched. Furthermore, also when it is folded into a compact standby style, it is hard to fold. If the base fabric is coated with silicone elastomer resin, the air bag is considerably more heat resistant and cold resistant than an air bag having a base fabric coated with chloroprene elastomer resin. Moreover, the amount of resin coated is only 40 to 60 g/m.sup.2, thus allowing a reduction in weight and an improvement in appearance and foldability. However, as yet, such improvement is not regarded as sufficient. Furthermore, the coating or lamination with an elastomer resin requires a complicated process, with attendant problems in productivity.
In addition, it is also demanded that the base fabric for air bags be less expensive and more easily folded for reducing the size of the module cover. Thus, air bags using non-coated base fabrics have attracted attention. In particular, high density non-coated air bags formed from woven fabrics of polyamide fibers such as nylon 66 and nylon 6, and polyester fibers have been tested and found to have improved mechanical properties and foldability as compared with air bags formed from coated base fabrics. However, they become frayed during sewing and are not low enough in air permeability, i.e., not high enough in gas interceptability, and intensive studies are being made to solve these problems. For example, JP-A-64-070247 proposes a pressure-compressed base fabric. However, this does not sufficiently prevent fraying, even though it is lower in air permeability. Furthermore, JP-A-07-040798 and JP-A-0-503763 propose a base fabric formed from a urethane resin. In particular JP-A-07-040798 discloses an air bag having a base fabric coated by dipping into an emulsion of a urethane resin and subsequently treated with a fireproof agent. However, even though such air bags are highly improved from the point of view of prevention of fraying, they are not low enough in air permeability, especially since the air permeability is increased by thermal deterioration, so that maintenance of air permeability at a stable, low level cannot be assured.